Ruger semi-auto locked open

Hello and hope someone can help.
I have an early .44 mag. Ruger carbine. It is in super shape but the slide locked open when I shot it. It wasn't the last round. I managed to get it taken down and freed the slide so it worked. I didn't bend or pry anything.
I pulled the slide open and it locked open again. It will not go shut when I depress the under button. I believe I was using pistol ammo in this older version. Is this repairable by a gunsmith?
I already know the factory no longer has parts per inquiry with Ruger customer service.

The ruger carbine runs much like a semi auto shot gun. (think Rem 11-87) its tube fed. When the gun fires, the bolt carrier moves the cartridge stop and the next round loads on to the carrier (or lifter) at the back of the carrier is a trip lever that allows the carrier unlock and move upwards and the bolt to move forward. If no round is in the tube then the trip lever is never hit and the bolt stays back bc the carrier stays down and it intercepts a notch in the bolt holding it in place. The one I fixed a while back was a bad cartridge stop timing. i the cartridge stop was interfering with the feed of the next round, slowing it down. Broken mag tube spring could also be a problem. If its weak it wont feed the next round with enough force to hit the trip lever nor fully feed the round to the carrier. The final thing could be trip lever is bound to the carrier for some reason and does not break away easily. The gun is easy to strip but repair of the trigger group and the timing can be rather tricky

Thank-you All for your comments...I have discovered the culprit. I looked into the lifter mechanism. What I discovered was the lifter latch has a pin other than the hinge pin that keeps the lifter from moving until you depress the lifter latch to load it or the gun fires.
This pin had slid all the way to one side keeping the lifter from operating (couldn't feed next shell). The gun thought it was in the "last round mode". It appears to be a simple fix if I can tighten the pin in the lifter latch......any suggestions?